Bash Scripting
Bash Scripting

Bash Scripting

Syntax

Define interpreter #!/bin/bash shebang (#!) with path to interpreter
 
Variables
ANY_VARIABLE=there

echo Hello $ANY_VARIABLE
 
Piping Take the output of the first command and pass to the next: ls -l /usr/bin | grep bash Gets a large list of files from /usr/bin then searches all for the bash keywords
 
Test Operators [ 5 = 5 ] = 0, 0 means it was executed without issue [ 3 = 5 ] = 1, 1 means it had one error [ 1 -eq 1] = 0, This tests the values match but will error if types mismatch
 
If/Else
if [ ${1,,} = marco ]; then
			echo "polo!"
elif [ ${1,,} = help ]; then
			echo "say marco to find me"
else
			echo "I'm hidden"
fi
 
Case (Switch)
case ${1,,} in
        admin | administrator)
                echo "Hi boss"
                ;;
        help)
                echo "Enter role"
                ;;
        *)
                echo "Not the boss"
esac
 
For Loop
for i in {1..5}
do
   echo "Welcome $i times"
done
 
Functions
showuptime(){
        local up=$(uptime -p | cut -c4-)
        local since=$(uptime -s)
        cat << EOF
-----
This Machine has been up for ${up}
It has ben running since ${since}
-----
EOF
}
showuptime
Note: Scope variables locally otherwise they could collide anywhere in the system globally
 

Vim

i INSERT (Before the cursor)
a APPEND (After the cursor)
esc Return to command mode
:wq write to disc & quit
:q! Quit without saving any changes
 
 

General Terminal

echo <arg> Displays arg parsed in the terminal cat <file> Displays contents of a file in the terminal
bash <filename>.sh Run shell file
pwd Print current working directory (More than ~/foo)
grep <keyword> <file/place> Search place for keyword ls -l | grep <keyword> Search keyword in list output
echo Foo! > bar.txt Overwrites “Foo” to a file echo Foo! >> bar.txt Adds “Foo” to a file
rm <file> Remove file
 
 

Misc.

File Permissions If you receive ‘Permission denied’ when running a file, type ls -l (To see the extended file info) and note the permissions: rw-r--r-- 1 fvm staff 1 1 Jan 10:30 shelltest.sh`
Now run chmod u+x <file> (u+x allows the owner to execute the file), note the permission changed: rwxr--r-- 1 fvm staff 1 1 Oct 10:30 shelltest.sh
 

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